Consider the scenario during the on-site survey, as described in Fig. REF (a), the receiver will be placed stationary during fingerprint registration so that it can obtain a more robust representation [1]}.
For example, we can put the receiver on the robot arm and the robot arm will remain stationary during the registration process.
We can also have the receiver held by a tripod or placed on the floor.
However, it is impossible for the user to hold her/his smartphone the same way the receiver was placed during the on-site survey, not to mention that the user does not even have the knowledge about the process of the on-site survey.
From Fig. REF (b), we can see that the smartphone is always held at different heights from the initial position where the fingerprint is registered.
So, even though the user stands on the exact same grid point where the fingerprint is registered, the observation vector always looks dissimilar to the fingerprint stored in the database.
While this subtle difference in distance from the initial position seems negligible, it was observed that a small change in distances may result in a very different RSS value even though the user remains still at the same grid point.
While many works have studied the variation induced by the environmental factors (e.g., multipath [2]}, [3]} and shadowing effects [4]}, [5]}), there are no work studies such a discrepancy.
